Amplifying devices for increasing the amplitude of faint or distant sounds are well known. U.S. Pat. No. 3,243,525, issued to Eaton on Mar. 29, 1966 teaches such a device. A somewhat similar device to correct for a user's hearing loss is taught in U.S. Pat. No. 3,894,195, issued to Kryter on July 8, 1975. Such devices should prevent damage to the user's ears and circuit elements when the microphone element is directed toward an unusually loud sound source.
While the art is aware of dynamic range compressing circuits for rendering all sounds (whether loud or soft) at a constant amplitude, the output of such a circuit lacks much of the character of the original sounds. Other known circuits employ filters to reduce the amplitude of certain aspects of the signal without affecting other portions of the signal. While such filtering circuits can be tailored to a particular application, a listening device including filtering circuits adapted for a wide variety of uses would inevitably filter out some desirable sounds and pass some objectionable sounds. The Kryter patent identified previously does disclose the concept of reducing the gain of an amplifier if an incoming signal exceeds a predetermined amplitude, recovering when the signal returns to a more moderate amplitude. But Kryter does not illustrate a circuit for accomplishing this aim.